Flexible joints make use of at least one flexible joint element, in particular a laminated joint, e.g. a ball joint made up of alternating layers of metal and of rubber.
The combination of large variations in pressure together with the action of gas dissolved in the fluid being conveyed leads to problems of bubbles of gas absorbed within the rubber decompressing rapidly.
U.S. Pat. No. 5,133,578 relates to a ball joint between two moving tubes (a so-called “floating” connection) using two symmetrical laminated ball joints and a central compensation system. In its FIG. 2, provision is made to protect the laminated joint by means of a metal bellows that transmits the outside pressure by varying in diameter, the bellows being in hydrostatic equilibrium. That bellows must therefore perform two functions simultaneously: it must track the movement of the laminated joint and it must also transmit pressure.
Such a bellows presents two main drawbacks, namely relative fragility and difficulty of fabrication because of its complex shape and its small thickness.
As an alternative, the above-mentioned patent proposes compensating pressure with the help of an accumulator (FIG. 4) or else of a piston housed in the central portion of the bellows (FIG. 5). Neither of those solutions is satisfactory.
Using an external accumulator associated with a leaktight high pressure connection raises problems of reliability in an undersea application, while implementing a piston complicates both structure and assembly and requires two bellows to be present with leaktight anchoring.